MOTS-c vs Thymosin alpha-1
Sold as a way to get the benefits of exercise without training. Mice given it stayed lean and ran longer, but it has not been tested in people. A peptide sold by wellness clinics as an immune booster. Trials show a modest effect in hepatitis B, and a large sepsis trial found none.
Thymosin alpha-1 has the stronger evidence, grade B (some human evidence) against grade C for MOTS-c. Neither is FDA approved.
Evidence
CAnimal and cell studies
BSome human evidence
Human studies cited
Animal or cell studies cited
Why the grade
The efficacy data are in mice: the 2015 discovery paper showing protection from diet-induced obesity and insulin resistance, and a 2021 paper showing better physical performance in young and old mice. The only human data measure the body's own MOTS-c rising in muscle and blood after exercise. No human has received MOTS-c in a published trial, so C.
Thymosin alpha-1 has several randomized trials in chronic hepatitis B (98 and 316 patients) and a meta-analysis of five trials with 353 patients showing delayed viral suppression, which is the approved use abroad. The 1,106-patient TESTS phase 3 trial in sepsis found no mortality benefit. The general immune-boosting use it is sold for in the US has no controlled trials, so the compound grades B on its hepatitis B evidence and D on the wellness claims.
FDA
Not approved
Not approved by the FDA for any use and sold as a research chemical. MOTS-c was placed in Category 2 (significant safety risk) in 2023; the nomination was withdrawn, the FDA removed it from that category in April 2026, and the Pharmacy Compounding Advisory Committee voted in July 2026 to recommend it for the compounding list. On 28 October 2026 HHS issued an enforcement discretion policy covering injectable MOTS-c acetate compounded by licensed pharmacies and physicians for named patients under sourcing, testing, labeling and reporting conditions. That is not an approval. It is also on the 2026 WADA Prohibited List.
Not approved
Thymosin alpha-1 is not approved by the FDA for any use. It is approved as thymalfasin (Zadaxin) in more than 35 other countries for hepatitis B and C and as an immune adjuvant. In the United States it was taken off the FDA's Category 2 compounding list after its nominators withdrew it, and in December 2024 the Pharmacy Compounding Advisory Committee voted 17 to 4 against adding it to the 503A bulks list; it is sold online as a research chemical.
Sold for
MOTS-c is sold as an 'exercise mimetic', a mitochondrial peptide said to burn fat, improve insulin sensitivity, and boost endurance the way training does.
Thymosin alpha-1 is sold by wellness clinics as an immune-system booster for infections, cancer support, autoimmune disease and long COVID.
Studies say
Mice given MOTS-c resisted obesity and ran longer, and humans make more of it after exercise, but no trial has given it to people, so the evidence is grade C.
Randomized trials support a modest, delayed antiviral effect in chronic hepatitis B, a large trial found no benefit in sepsis, and there are no trials of the immune-boosting uses marketed in the US, which is why it grades B.
Class
Mitochondrial-derived peptide
Immunomodulatory peptide
Route
Injection
Injection